As represented for example in FIG. 1, a repetition device 1 aboard a satellite 2 generally comprises microwave signal transmit and receive chains intended to convey, amplify and route the signals between a terrestrial station and users located in specific geographical zones. On reception, the signals received by the receive antenna 3 are sent to a receiver 4 by way of a receive filter 5 and then amplified by amplifiers 6 and re-transmitted, after passing through a transmit filter 7, by a transmit antenna 8. For technical amplification reasons, before amplification, the bandwidth of the signal received is divided into several sub-bands of reduced width equal to those of the user channels by way of a demultiplexing device 9 conventionally called an IMUX (for Input Multiplexor), and after amplification, the amplified signals are recombined into a single broadband signal. The recombining of the signals into a single output broadband signal is generally carried out by means of an output multiplexing device 10 conventionally called an OMUX (for Output Multiplexor) which comprises several elementary filters 11, each elementary filter having a predefined central frequency and bandwidth.
As represented for example in FIG. 2, each filter 11 comprises a signal input 13 and a signal output 14, the filters being connected in parallel with a common output port 15 by way of a transverse waveguide 16, called a manifold, which links together the outputs 14 of all the channels. Each filter 11 comprises at least one resonant internal cavity or several resonant internal cavities coupled together, for example by way of coupling irises so as to form a channel in which the RF radiofrequency signals travel.
The various filters 11 of the OMUX are conventionally fixed horizontally and in parallel to one another on a thermally conducting, and generally metallic, common support 12 in such a way that the longitudinal axis Z of each channel is substantially parallel to the plane of the support 12. The longitudinal walls of each cavity are then in contact with the support 12, either directly or by way of fixing brackets 7 thereby making it possible, by thermal conduction, to be able to remove the thermal energy dissipated by the cavities of the filter 11 to the support 12. Conventionally, the thermal flux crosses the support 12 perpendicularly to the filter 11 toward heat pipes disposed on a panel of the satellite.
In the nominal operating mode corresponding to operation of the filter in the frequency band for which it is dimensioned, this thermal energy is essentially due to losses by skin effects due to a Joule effect in the walls of the filter, these losses being dissipated by conduction from the interior to the exterior of the filter. In an operating mode called “off-band” corresponding to an anomaly in the transmission frequency around a filter of the OMUX, the filter operates outside of the frequency band for which it is dimensioned. In this off-band operating mode, the filter absorbs and dissipates a large part of the energy of the signal. The power dissipated by the filter in the off-band operating mode is of the order of three higher than in the nominal operating mode. In the case where the OMUX is of the thermocompensated type and where each filter comprises a flexible membrane making it possible to control the volume of the cavity and thus to adjust the operating frequency as a function of temperature, this large power dissipation can have a penalizing effect on the flexible membrane since this part is highly resistive and generates strong temperature gradients.
The channels of the filters of an OMUX are therefore always dimensioned thermally with respect to the off-band mode.
A horizontal architecture of the OMUX is very suitable for the control of the thermal gradients of the channels, but remains limiting for meeting the new requirements encountered within the framework of space applications since, on the one hand, in the case of an application requiring very large powers, greater than or equal to 500 W, this architecture generates significant thermal flux densities at the interfaces of the off-band channel on the heat pipes of the panel of the satellite, which means there is a risk of these heat pipes drying out; on the other hand, this architecture requires a large installation footprint in the plane of the support, this being penalizing in the case of an arrangement of payloads in a very limited bulk.
To solve the problem of the flux density constraints on the heat pipes, it is conventional to develop overdimensioned heat pipes, thereby penalizing the arrangement of the payload of the satellite.
To solve the problem of the OMUX bulk and to optimize its installation, the vertical architecture may be preferred to the horizontal architecture, but it causes much more significant thermal gradients than those obtained with a horizontal architecture. Currently, a known solution for solving this thermal gradient problem consists in increasing the conductive cross section of each channel by increasing the thickness of the walls of each filter. However this requires consequent additional material which significantly increases the mass of the OMUX, this being penalizing, or indeed prohibitive, for space applications.
The aim of the invention is to produce a microwave channel multiplexing device optimized in mass making it possible to decrease the thermal flux density at the interface of the off-band channel, notably in the case of an application requiring very large powers.